Field
The present application describes various exemplary devices, systems and surgical techniques for achieving access to a site within the body, particularly the spine. More particularly, the present application describes a system and device components for providing a minimally invasive retractor system for directly viewing and accessing a surgical site in the body, particularly the spine. In some exemplary embodiments, the system and device components are useful for accessing the spine for one or more purposes of manipulation, removal, replacement and reinforcement of intervertebral discs, particularly in the lumbar spine. According to such embodiments, the present invention overcomes shortcomings in the art.
Description of the Related Art
A common surgical approach for addressing spinal injuries and pathologies involves placement in the spine of one or more mechanical devices to enable clinical interventions for correcting the spine that include intervertebral stabilization, distraction, decompression, joint fusion and combinations of these. There are a variety of such mechanical devices. For example, implants referred to as interbody devices are inserted between two adjacent vertebrae within the space that is naturally occupied by the disc. Other devices, such as screws, plates, rods, and tethers are also used in various combinations, sometimes together with interbody devices, to achieve desired correction to the spine. Specialized instrumentation is required for implantation of each of these devices, and a wide range of surgical techniques and modes of access to the spine have been developed, presenting a large array of options and complexity for neurosurgeons and orthopedists who specialize in the spine.
Broadly, there are at least three general modes of access to the spine for achieving delivery of spinal correction devices. These general modes include anterior (through the abdominal cavity), posterior (including transforaminal), and lateral (including extreme lateral). For example, in the context of lumbar surgery, the lexicon includes the following terms that describe these various modes of access for achieving fusion between lumbar vertebrae: anterior mode of access is known as “ALIF” (Anterior Lumbar Interbody Fusion); posterior mode of access is known as “PLIF” (Posterior Lumbar Interbody Fusion); an alternate, minimally invasive posterior mode of access is known as “TLIF” (Transforaminal Lumbar Interbody Fusion); and lateral mode of access is know as “DLIF” (Direct Lumbar Interbody Fusion), including a minimally invasive lateral mode known as “XLIF” (eXtreme lateral Lumbar Interbody Fusion). Selection of the mode of access for a particular patient is dictated by a number of factors, including the extent of correction needed, the location within the spine requiring correction, and the preference and skill of the surgeon.
As with most other areas of surgery, is it preferable when operating on the spine to employ the least invasive surgical approach possible for achieving correction to minimize trauma and associated pain and blood loss experienced by the patient, to improve recovery time and outcomes, and to reduce operating room time and costs. Thus, while good results have historically been achieved through full-open access to the spine (typically through one of anterior and posterior routes), there is significant attention to developing minimally invasive surgical approaches. Each of the various open and minimally invasive techniques involve specialized instrumentation for achieving surgical access, and particularly for the minimally invasive approaches, specialized devices have been developed that are adapted for delivery according to the selected technique and the associated instrumentation.
In accordance with the various methods of spinal access, there are several commonly shared requirements and steps. In all cases, it is necessary for the surgeon to determine the proper size of the disc space (or spaces) to be accessed so as to select appropriately sized implant(s); this is typically achieved with preoperative imaging, in particular, MRI and CAT scans. And a fluoroscopy machine (C-arm) is on hand to provide real-time x-ray images, particularly in those procedures where the spine cannot be directly visualized due to impedance of soft tissue or small surgical field. In some instances, neuro-monitoring equipment is used to ensure that the instrumentation and implants are not causing damage to spinal nerves. This equipment typically measures spinal nerves indirectly by monitoring changes in leg muscle reflexes over time.
In all modes of approach, one or more special retractors and tubes are typically used to dissect and displace tissue and expose the vertebrae, and other instruments are used to release the annulus and open the disc space, remove disc material, and prepare the space to receive an implant. Thereafter, one or more interbody implants is inserted in the prepared space, typically together with one of a variety of bone graft and osteogenic materials. In some examples, the implants are secured to one or both vertebral end plates using screws. During the procedures one or multiple levels of fusion may be completed. Beyond these common steps, there is a good degree of variation in technique and instrumentation for each of the modes of spinal access.
Anterior Access
Anterior Lumbar Interbody Fusion involves access to the spine from the front (anterior) of the patient's body, usually through an incision in the lower abdominal area or on the side. ALIF may be executed as a full-open procedure or as a minimally invasive procedure, for example, using laparoscopes, and involves cutting through, and later repairing, the muscles in the lower abdomen, and retracting (temporarily moving or displacing) muscles and blood vessels to gain access to the spine. ALIF advantageously allows for direct access to the disc space at all vertebral levels without need to resect spinal bone and without trauma to posterior muscles and nerves. Delivery of large sized implants is possible via ALIF. Disadvantageously, for all ALIF procedures, the patient must be in a supine position (on her/his back). Because it does not allow for posterior access to install pedicle screws, rods, tethers and other implants that stabilize the spine, the patient must be repositioned from supine to prone after the ALIF procedure is completed in order to gain posterior access to the spine. Repositioning typically extends the time in the operating room and can introduce additional risk. Further, ALIF access typically requires the involvement of other surgeons, such as general surgeons, adding time and cost to the procedure.
Posterior Access
Posterior Lumbar Interbody Fusion allows the vertebrae to be reached through an incision in the patient's back (posterior). PLIF may be executed as a full-open procedure or as a minimally invasive procedure. One of the perceived key advantages to this approach is that the spine is accessed while the patient is in a prone position on the operating table, thus avoiding the need for the patient to be repositioned on the table after an ALIF procedure, and allowing interbody placement to be achieved in parallel with pedicle screw and rod placement (i.e., implantation of the interbody device at the same time as other fixation devices). PLIF typically involves a 3-6 inch incision in the patient's back and retraction of the spinal muscles and nerves to allow access to the target intravertebral space, typically followed by removal of a portion of the vertebra called the lamina (laminectomy) and as needed, some portion of the facet joints. Thereafter, the affected disc material is removed to accommodate implantation of the interbody device and bone graft material. There are advantages to this surgical approach, including avoidance of the need for patient repositioning, and possibly improved rates of fusion due to the ability to achieve greater compression. Some of the disadvantages include risk of retropulse of the implant into the canal which can cause neural compression, and incomplete clearance of the disc space due to access limitations posed by posterior bone.
Transforaminal Lumbar Interbody Fusion is a refinement of the PLIF procedure and has recently gained popularity as a minimally invasive surgical technique for conditions affecting the lumbar spine. The TLIF technique involves approaching the spine in a similar manner as with PLIF but the spinal target site is displaced laterally, away from the posterior centerline of the spine and toward the side of the spinal canal. As compared with PLIF, this approach enables a relatively reduced amount of surgical muscle dissection and nerve manipulation to access the disc space. And as compared with ALIF, this approach does not require the presence of a general surgeon, or the risks involved in access through the peritoneal cavity, or the need for rotation of the patient. A key disadvantage to this mode of access is the requirement for blunt dissection through the psoas muscle and the attendant problem of compression or dissection damage to nerve tissue that runs through the psoas muscle. This is particularly a problem since the field of view available in the TLIF technique is very limited making accurate identification of the nerve tissue a challenge.
Lateral Access
Direct Lumbar Interbody Fusion, and the minimally invasive counterpart, Extreme Lateral Lumbar Interbody Fusion, avoids an incision to the abdomen and avoids cutting and disrupting the muscles of the back. According to this mode of approach, the disk space is accessed from a very small incision on the patient's side (flank). The patient must be in a lateral recumbent or recovery position (on her/his side). As compared with PLIF, this approach reduces the amount of surgical muscle dissection and is intended to minimize the nerve manipulation required to access the intervertebral space. And as compared with ALIF, this approach does not require the presence of a general surgeon, or the risks involved in access through the peritoneal cavity. But DLIF/XLIF specifically presents some of the same challenges as TLIF in terms of trauma to the posas muscle and possible neropraxia due to compression caused by the retraction instruments. And because the procedure does not allow posterior access, any procedures that require direct posterior access must be done serially rather than in parallel with the interbody implantation.
Posterior Lateral Access
Other less invasive lateral-type approaches have been developed or proposed using posterior entry and lateral access to the spine via a curvilinear path. Such systems rely on fixation of the instrumentation/retractor either at its proximal end (i.e., proximate to the surgeon, outside the patient's body) to structures having positions that are fixed relative to the spine (i.e., instruments that are fixed in space either through attachment directly to the spine or to other fixed position structures), or at more than one location at the distal end (such as, for example, dorsal and ventral tangs that pierce into the disc and/or inferior/posterior pins that engage with each of the adjacent vertebra. Experience with such systems that have actually been manufactured has shown that reliance on such fixation does not effectively maintain the position of the curvilinear refractor at the spinal access site (ie, the instrument's portion that is distal relative to the surgeon), resulting in significant slippage and/or displacement of the retractor from the spine during manipulations and implant placement. Moreover, the visualization that is achieved using substantially tubular curvilinear retractors is quite poor and impractical for the useful conduct of surgical procedures within the disc space.
While the overall curvilinear shape and the use of fixation means are intended to enable posterior lateral access, such systems are essentially rigid assemblies that don't allow the surgeon to manipulate soft tissue in order to optimize positioning and securement, provide only a limited effective view of the surgical field due to the relatively closed nature of the portal, and they don't ameliorate the concussive forces involved in tissue removal and implant delivery. These and other disadvantages with existing posterior-lateral instruments and approaches preclude the successful implementation a surgical approach that is otherwise favorable for overcoming many of the limitations and disadvantages of the TLIF, XLIF, and PLIF procedures and instruments.
There is a need for a surgical approach and associated instrumentation and devices that avoid the existing complications known in the art with the various modes of spinal access. More specifically, there is a need for advances with instrumentation and surgical technique to allow for the more desirable prone patient positioning during spinal access surgery combined with the benefits of lateral access to the target intervertebral space.